1. Field of Invention
This invention relates to a floppy disk cartridge, and more particularly to the floppy disk cartridge wherein a waving phenomenon which occurs at high speed rotation of a magnetic disk rotatably incorporated in the floppy disk cartridge can be absorbed, thereby allowing a smooth rotation of the magnetic disk.
2. Related Art
A conventional floppy disk cartridge of the type will be described referring to FIGS. 5 and 6. FIG. 5 is a front view of the floppy disk cartridge 1 (hereinafter referred to as xe2x80x9cFD cartridgexe2x80x9d) taken in a vertical section traversing a position of a head window 2, and FIG. 6 is a rear view showing an inner face of a lower shell 3b. In FIG. 5, the FD cartridge 1 consists of an upper shell 3a and the lower shell 3b attached to each other, and a magnetic disk 4 rotatably incorporated between the upper and lower shells. The magnetic disk 4 is incorporated in the FD cartridge 1 with its center hub 5 inserted in a hub opening 6 which is formed in the central part of the lower shell 3b. 
Liners 7, 7 formed of a soft cloth-like sheet are respectively attached to the inner face of the upper shell 3a except the head window 2 and the area facing with the hub opening 6, and to the inner face of the lower shell 3b except the head window 2 and the hub opening 6. The liners 7, 7 are provided for the purpose of protecting respective media faces on both upper and lower faces of the magnetic disk 4 so as to keep the media faces free from scratches or the like.
When the magnetic disk rotatably incorporated inside the conventional FD cartridge performs a high speed rotation, gaps between the magnetic disk and the upper shell and the lower shell abruptly change by the head window part to cause a waving rotation of the magnetic disk. On such occasion, there would be a fear that the magnetic head might not stably contact or float with respect to the magnetic disk which is rotating at high speed, and would not be able to obtain accurate reading and writing on the magnetic disk.
Accordingly, there has arisen a technical problem which should be solved to attain a smooth rotation of the magnetic disk by preventing an occurrence of the waving phenomenon even when the magnetic disk in the FD cartridge rotates at high speed, and it is an object of the invention to solve the problem.
This invention is proposed to attain the above described object, and to provide a floppy disk cartridge which comprises an upper shell and a lower shell, a magnetic disk rotatably incorporated between the upper shell and the lower shell, head windows provided at respective one sides of the upper shell and the lower shell so as to face with each other, and liners respectively attached to inner faces of the upper shell and the lower shell except the head windows for protecting the magnetic disk, provided in that at the inner face of either one of the upper shell and the lower shell are formed concave portions along both left and right side edges of the head window, and that the liner is attached to the inner face of the upper shell or the lower shell from respective outer edges of the concave portions.
According to the invention, there are formed concave portions at both sides of the head window at the inner face of either of the upper shell and the lower shell of the FD cartridge. Therefore, when the FD cartridge is inserted into the floppy disk drive and the magnetic disk in the FD cartridge is rotated at high speed, the negative pressure will be created in the concave portions with the high speed rotation of the magnetic disk. Then, the magnetic disk which is rotating at high speed will be drawn toward the concave portions by the negative pressure. Thus, such waving rotation as occurring in the conventional floppy disk cartridge will be inhibited and the smooth high speed rotation of the magnetic disk can be anticipated. In this way, the invention can attain significant effects that stable contact or floating of the magnetic head with respect to the magnetic disk can be obtained thereby to perform accurate reading and writing.